Rubber modified styrene-based resins are widely employed in the production of interior and exterior components for electric and electronic appliances and office automation equipment due to their good workability and mechanical strength.
However, rubber modified styrene-based resins have no resistance against combustion. Further, rubber modified styrene-based resins can actually fuel flames because the resins function as an energy source and promote combustion when a flame is ignited by external ignition factors. For this reason, legal regulations in many countries, including the United States and the European Union, require that resins used in interior and exterior components for electric and electronic appliances meet flame resistance standards. Accordingly, there is on-going research directed to imparting flame resistance to rubber modified styrene-based resins.
A flame retardant, such as a halogen-based flame retardant, a phosphorous-based flame retardant or an inorganic flame retardant, and a flame retarding aid can be added to rubber modified styrene-based resins to impart flame resistance thereto. However, impact resistance deteriorates when a large amount of a flame retardant is added to a rubber modified styrene-based resin to provide flame resistance.
Currently, electric and electronic appliances and office machines are becoming increasingly larger and thinner. When rubber modified styrene-based resins are used in the production of larger thinner products, however, impact resistance and stiffness of the rubber modified styrene-based resins fall short of required levels for such extra-large thin products. Therefore, there is a need to improve the impact strength of such products, for example as determined using a falling ball impact strength test.
Polyester resin generally has a structure with a short molecular chain and is not easily bent. Accordingly, polyester resin has good stiffness, electrical properties, weatherability and heat resistance. Also, the tensile strength of polyester does not significantly deteriorate even when the polyester resin is exposed to a high temperature for a long period of time. In addition, polyester resin has good resistance against oil, such as diesel oil, due to its crystalline nature.
However, the physical properties of polyester resin can change easily when it is brought into contact with an acid or alkali at a high temperature for a long time since the polyester resin has an ester bond. Therefore, polyester resin should be reinforced, for example with glass fiber, when the polyester resin is used as a structural material. Otherwise, it is difficult to use a conventional polyester resin as a structural material formed by injection molding.
Polyester resin can be decomposed at a very fast rate during the combustion thereof. Therefore, it is very difficult to prepare a flame resistant polyester resin. Since it is very difficult to prepare a flame resistant polyester resin from the polyester resin alone, polyester resin comprising reinforcements such as glass fiber is frequently used to provide flame resistance.
Polyester resin has been alloyed with rubber modified styrene-based resin in an attempt to prepare a flame resistant polyester resin. The alloyed resin, however, cannot be used as a structural material due to its significantly deteriorated impact resistance.